Enhance README with detailed testing instructions and clarify world generation process; implement chunk boundary handling in OsmWorldBuilder; integrate Vitest for testing in the web project; add theme toggle functionality and improve styling in the web interface.

tests/TheLivingWorld.Tests/ImportPipelineTests.cs

@@ -55,10 +55,11 @@ public class ImportPipelineTests
     [Fact]
     public void Imports_a_highway_as_a_road_with_a_width()
     {
+        // Kept inside a single chunk so this test is about the attributes, not the splitting.
         using var world = Build(WayWithGeometry(
             id: 7,
             tags: new() { ["highway"] = "residential", ["name"] = "Main Street" },
-            metres: [new Vector2(-200, 0), new Vector2(200, 0)]));
+            metres: [new Vector2(100, 0), new Vector2(300, 0)]));
 
         var road = Assert.Single(Export(world)[0].Chunk.Roads);
 
@@ -76,12 +77,50 @@ public class ImportPipelineTests
             tags: new() { ["highway"] = "primary" },
             metres: [new Vector2(0, 0), new Vector2(50_000, 0)]));
 
-        var road = Assert.Single(Export(world)[0].Chunk.Roads);
-        var maxX = road.Path.Where((_, index) => index % 2 == 0).Max();
+        var maxX = Export(world)
+            .SelectMany(chunk => chunk.Chunk.Roads)
+            .SelectMany(road => road.Path.Where((_, index) => index % 2 == 0))
+            .Max();
 
         Assert.True(maxX <= WorldSizeMeters / 2 + 0.5, $"Road reached {maxX} m, past the world edge.");
     }
 
+    [Fact]
+    public void Splits_a_long_road_into_one_piece_per_chunk_it_crosses()
+    {
+        // Spans the full width of the world at y = 0, which crosses all four chunk columns of row 2.
+        using var world = Build(WayWithGeometry(
+            id: 12,
+            tags: new() { ["highway"] = "primary" },
+            metres: [new Vector2(-900, 0), new Vector2(900, 0)]));
+
+        var chunks = Export(world);
+
+        Assert.Equal(4, chunks.Count);
+        Assert.All(chunks, chunk => Assert.Equal(2, chunk.Coord.Y));
+        Assert.Equal([0, 1, 2, 3], chunks.Select(chunk => chunk.Coord.X));
+
+        // Every piece now sits inside its own chunk, so the chunk's bounds no longer stretch across the map.
+        foreach (var chunk in chunks)
+        {
+            var square = world.Grid.BoundsOf(chunk.Coord);
+            Assert.True(chunk.Index.Bounds[0] >= square.MinX - 2f);
+            Assert.True(chunk.Index.Bounds[2] <= square.MaxX + 2f);
+        }
+    }
+
+    [Fact]
+    public void Keeps_a_short_road_whole()
+    {
+        using var world = Build(WayWithGeometry(
+            id: 13,
+            tags: new() { ["highway"] = "service" },
+            metres: [new Vector2(10, 10), new Vector2(60, 40)]));
+
+        Assert.Single(Export(world));
+        Assert.Single(Export(world)[0].Chunk.Roads);
+    }
+
     [Fact]
     public void Assembles_a_multipolygon_relation_and_keeps_its_holes()
     {
@@ -147,13 +186,13 @@ public class ImportPipelineTests
     }
 
     [Fact]
-    public void Chunk_bounds_stretch_to_cover_geometry_that_overhangs()
+    public void Chunk_bounds_stretch_to_cover_areas_that_overhang()
     {
-        // A road whose centre sits in one chunk but which reaches well into its neighbours.
+        // Areas are still bucketed whole by the centre of their extent, so a large one overhangs its chunk.
         using var world = Build(WayWithGeometry(
-            id: 12,
-            tags: new() { ["highway"] = "primary" },
-            metres: [new Vector2(-900, 0), new Vector2(900, 0)]));
+            id: 14,
+            tags: new() { ["landuse"] = "forest" },
+            metres: Square(0, 0, 1500, closed: true)));
 
         var exported = Assert.Single(Export(world));
         var square = world.Grid.BoundsOf(exported.Coord);